Bicomponent fibers are known in the art, and such bicomponent fibers, as the term is used herein, comprise two polymer materials of different chemical nature which are combined in some fashion such that each of the two polymers is discretely identifiable in a particular portion of the overall fiber structure. Examples include core-and-sheath fibers, side-by-side fibers, and island-in the-sea fiber among others. While such bicomponent fibers are generally made of combinations of polyesters, polyamides, polyamides, liquid crystalline polymers and others polymeric materials, at least one bicomponent fiber has been described which comprises cellulose acetate and a second polymer material.
U.S. Pat. No. 5,509,430 to Berger describes a core-and-sheath type bicomponent fiber in which a sheath of cellulose acetate surrounds a core of polypropylene. The bicomponent fiber is used to prepare tobacco smoke filter rods for use in cigarettes and other smoking products. Although cellulose acetate is an expensive material relative to other polymers such as polypropylene, it is used in such filters because its cost is offset by other factors such as having an acceptable filter efficiency, not significantly detracting from taste, having low resistance to draw and having sufficient, but not excessive, hardness.
Nonwoven products are also known in the art and such products have been made from many different materials including natural cellulose (e.g., wood pulp and cotton), polyolefins, polyesters and other polymeric materials. Examples of such products include disposable towels, diapers and other hygiene products. Since such nonwoven products are usually disposable, cellulose esters have not generally been used because of the cost of the cellulose ester material. For similar reasons related to the cost of the cellulose esters, bicomponent fibers having a cellulose ester sheath have not been prepared and used in such products. Lastly, because cellulose ester fibers are generally of low strength relative to other fibers such as polyolefins and polyesters, the cellulose ester fibers often cannot be used on high speed manufacturing machines because they undergo excessive breakage resulting in manufacturing downtime. However, because cellulose esters have certain desirable properties, particularly with regard to fluid acquisition and absorption, and the ability wick fluids from one site to another, cellulose ester fibers and cellulose ester sheathed bicomponent fibers present unique opportunities in the preparation of nonwoven materials.
Accordingly, one purpose of this invention is to describe nonwoven materials and methods of preparing same which utilize bicomponent fibers comprising a first cellulose ester polymer and a second, different polymer.
Another purpose of this invention is to describe nonwoven materials and methods of preparing same which utilize core-and-sheath bicomponent fibers having a sheath of a first cellulose ester polymer and a core of a second, different polymer.
In addition, it is also the purpose of this invention to describe absorbent products made of nonwoven materials which have improved fluid acquisition, distribution and retention properties due to the utilization of a bicomponent fiber comprising a first cellulose ester polymer and a second, different polymer.